Apparatus for the extraction of water soluble substances from fruit and vegetable pressings and vegetable raw materials

ABSTRACT

Apparatus for the extraction of fruit and vegetable pressings and plant raw materials in a closed system. The extraction is effected by simultaneous mechanical and hydrodynamic effects on the materials, the fruit or plant mass being subjected to several extractions in two cyclically alternating modes of fountain-type and turbulent agitation with different intensities with bladed agitator tip speeds in an over-all range of 3 to 25 m/sec. The apparatus has a closed heat-insulated vessel with internal draining wall, a conical bottom, a cover having a ventilation opening, and an opening for the raw material, with a driving unit mounted on the cover with two driving speeds. The driving unit is a shaft on the lower end of which there is mounted an impeller, the shaft resting on a special bearing supported on a grid of blades rectifying the material flow, an elongated diffuser surrounding the impeller, the impeller together with a suction unit leading to the diffuser being fixed to the bottom of the vessel.

This is a division of application Ser. No. 178,577, filed Aug. 15, 1980,now U.S. Pat. No. 4,370,473.

There are well known methods of extracting pectin substances from driedapplie pressings or citrus rinds. According to one method (Karakolev G.,I. Ognyanov, M. Marinov. Pektinovi Veshtestva. Nauka i Izkustvo, Sofia(1956).), the extraction vessel is charged with apple pressings whichare single or double washed by water with a slow agitation of themixture. After a one hour draining of the wash water with the mixture atrest, hot water and a suitable amount of mineral acid (sulphurous,hydrochloric, sulphuric, or nitrous acid) is added for carrying out theextraction accompanied by a slow agitation of the mixture for aspecified time. Then the extract is drained gravitationally, the mixtureagain being at rest. Hot water for a secondary extraction is added tothe residue. After an agitation of 30 minutes, the second extract isdrained off. Cold water is added to the residue for a third extraction.There then follows a draining of the third extract and a furtherpressing of the residue. The single or double washing of the rawmaterial is omitted when pre-washed apple pressings or citrus rindpressings are being extracted.

The above cited article by Karakolev et al also discloses an apparatusfor carrying out the method disclosed therein. Such apparatus includes awooden vessel covered by a lid which has an opening for feeding the rawmaterial thereinto. On such lid there is a driving unit which includesan electrical motor with a screw reducer for driving a vertical frameagitator. The agitator is submerged in the vessel liquor in a suspendedposition. The frame has several radial blades for increasing zones ofagitation of the material in the vessel. The vessel has a second innerwall or double bottom of perforated acid-resistant terracotta tiles usedfor gravitational draining.

The main deficiencies of the above described prior method and apparatusare, in the first instance, the low diffusion speed of the pectinsubstances from the vegetable tissue to the solvent. For this reason theextraction process is lengthy (from 8 to 14 hours) and the degree ofrecovery of the pectin is rather low (50 to 70%). The above describedapparatus fails to insure the intensive and even homogenization of themixture in all zones of the extractor, and furthermore considerablepower is needed to rotate the whole mass of the mixture in theextractor.

In another prior method (Kerteza, Z. I. The Pectic Substances.Interscience Publishers, New York (1951).) the raw material is subjectedto acid pre-treatment by hydrogen chloride or any other acid agent tobring the pectin to a soluble form, following which the whole extractionprocess takes place. In this manner the subsequent proces of diffusionis improved, but nevertheless no complete pectin extraction can beachieved. The raising of the temperature of extraction improves thedegree of extraction on the one hand, but on the other it reduces thejelly formation of the pectin due to resulting degradation processes.

Organic substance extraction from natural raw materials imposes specificrequirements for a short process in order to eliminate any possibilityfor concurrent undesired side chemical, physicochemical andmicrobiological processes. Experiments for accelerating the extractionby ultrasound effects have not yet resulted in any industrialapplications in the field of pectin production, due to poortechnological results and the low efficiency of the ultrasoundgenerators employed. Another manner of speeding up the process is toemploy continuous extraction in the counterflow. This method isdisclosed in (Owens, H. S., R. M. McCready and W. P. McLay. FoodTechnol., 3, 77 (1949).), and also in (Graham, R. P., A. D. Shepherd,Agricultural and Food Chemistry, 1, 16, 993 (1953).). No satisfactoryresults have been attained expecially in pectin production by means ofcounterflow extraction, mainly because of technological difficulties inthe manner of extraction, extract separation, and the safety of theapparatus.

A method and apparatus for the intensification of extraction fromvegetable raw material has been suggested in K. Marev, H. Krachanov, A.Bratanov, N. Kirchev-authors' certificate No. 24725, People's Republicof Bulgaria. This publication suggests such extraction by means ofperiodic short-term turbulent agitation of the extracting agent and themass of vegetable matter by a propelling mechanism which guaranteesrelatively high speed of movement of the mass (ranging from 5 to 20m/sec), and the transition of the mass from low pressure to highpressure zones, thus sharply accelerating the rate of the diffusion ofthe extracted substance. This method has been used with some success forthe extraction of some vegetable raw materials (such as coffee,soybeans, herbs, etc) but certain faults in the extraction of pectin,mainly in the apparatus, limit the employment of theoretically morebeneficial technological conditions in its operation. If the process isconducted in an ordinary cylindrical vessel of no special shape with aflat bottom, in the case of a lighter mode of agitation of the mass thisis accompanied by the formation of some insufficiently active zones ofthe extracting volume, thereby prolonging the process and reducing theefficiency of the method. When a more intensive agitation is employed,considerable crushing of the mass is produced, in becomes sticky andcannot drain easily. This also reduces the efficiency of the wholeprocess.

There are also well known methods of washing fruit and vegetablepressings after the separation of the natural fruit or vegetable juicefor increasing the juice yield, as well as an apparatus for carrying outsuch method, which are characterized by lamellar extracting agentflow-around the extractable particles. Such method and apparatus aredisclosed in Boney M. Tehonologiya na konserviraneto na plodovi izelenchukovi sokove i knotsentrati. plovdiv (1978). The defect of thesemethods and apparatus is that diffusion is greatly delayed, as a resultof which there is an insufficiently complete extraction of theextractable substance.

The present invention has among its objects the provision of a methodand an apparatus for the periodic extraction of extractable substancesfrom fruit and vegetable pressings and raw materials of vegetable originwhich guarantee the accelerated and complete diffusion of the watersoluble substances of the plant tissue to the extracting material bymeans of suitable physical and chemical effects, and the efficientextract separation by repeated raw material extraction.

In the method of the invention for the accelerated extraction of pectinand other extractable matter from plant material, the process is carriedout with continuous agitation of the entire volume of the mass in twomodes which differ in agitation intensity. In a preferred embodiment ofthe apparatus for carrying out such method the change of mode ofagitation is effected in cycles by an automatic machine with aprogrammed effect, such machine having a two-speed electric motor whichdrives a bladed propeller mechanism to produce a fountain-type turbulentagitation at relatively high propeller tip speeds in an overall range offrom 3 to 25 m/sec wherein the whole volume of the mass progressesrepeatedly through zones of different pressures and speeds. After suchagitation the extract is drained, and the mass is again extracted untilthe complete extraction of the extractable matter has been carried out.This permits the second extract to be used in a subsequent firstextraction, the third extract to be used for a subsequent secondextraction etc., whereby there is produced an extract of higher drysubstance concentration.

The invention will be more readily understood upon consideration of theaccompanying drawings, in which:

FIG. 1 is a view in vertical section through a preferred embodiment ofthe apparatus of the invention, certain of the parts being shown inelevation, and

FIG. 2 is a view in horizontal section through the apparatus of FIG. 1,the section being taken along the line 2--2 in FIG. 1.

The apparatus shown in FIGS. 1 and 2 has a circular cylindrical vessel 1the side walls of which are provided with a layer of heat insulation 2.The bottom of vessel 1 is frusto-conical in shape, the lower centralpart of which is connected to an outlet for the discharge of solidmaterial from the vessel. An upright screen 5 is disposed within thelower and intermediate parts of the vessel 1, the screen having arcuateportions spaced radially from the inner side wall of the vessel, sucharcuate portions being of equal angular extent and being separated byinwardly folded zones 5' of the screen. Outwardly of the screen 5 thevessel is provided with a side outlet 6 at the bottom thereof for theperiodic discharge of liquid extract.

Vessel 1 is provided with an upper cover or lid 7 having a closableinlet 8 for solid raw material to be introduced into the vessel. Cover 7also has an inlet 9 with a shut-off valve therein to provide for theinlet of liquid into the vessel. A manhole cover 10 is provided so thataccess may be had when needed to the interior of the vessel 1.

A vertical shaft 11 is journalled in a suitable bearing in the cover 7,shaft 11 extending downwardly to a lower end disposed somewhat above thelowest central portion of the bottom 3 of the vessel. Affixed to theshaft 11 near the bottom end thereof in an impeller or propeller 13.Surrounding the impeller 13 is a diffuser, generally designated 14, thediffuser having a sharply upwardly converging frusto-conical lowerportion 15, a circular cylindrical intermediate portion in the zonethereof immediately surrounding the impeller 13, and a graduallyexpanding frusto-conical upper portion 16 above 13. Immediately abovethe impeller 13 there is a bearing 12 for the lower end of shaft 11, thebearing 12 being mounted on the diffuser 14 through the medium of a massflow rectifying grid composed of a plurality of generally radiallyextending blades 12a the tips of which are attached to the inner sidewall of the diffuser at the circular cylindrical intermediate portionthereof. The blades of the impeller 13 and of the mass flow rectifyinggrid have opposite inclinations, as shown, whereby the mass issues fromthe upper end of diffuser 14 with little if any spin.

An injector-mixer 17, which is of the venturi pipe type, has a dischargepipe 18 leading downwardly therefrom and connected by a radiallyinwardly directed pipe extending through the wall of the vessel 1 to acentral injector ring 19 having spray jet creating openings in the lowersurface thereof, such openings being distributed around thecircumferential extent of the ring 19.

The shaft 11 bearing the impeller 13 is driven by an electric motor 20through a first pulley 21 disposed on the drive shaft of the motor, asecond pulley 22 affixed to the upper end of the shaft 14, and a belt 23driving the connecting pulleys 21 and 22. The electric motor 20 is underthe control of control means mounted in a cabinet 24, as shown.

The above-described apparatus operates as follows.

The closed vessel 1 is filled with water or other liquid solventsthrough pipe 9 and with raw material through opening 8. At the sametime, the shaft 11 is set rotation by energizing the motor 20 throughthe control means 24. The driven shaft 11 turns the impeller 13 as aresult of which the fluid mass is sucked via the conical part 3 of thevessel 1 through portion 15 of the diffuser from which it flows past theimpeller 13. In its flow upwardly, the mass is forced past thestationary blades 12a which rectify its flow; the mass then continuingthrough the upper part 16 of the diffuser and eventually reaches theupper surface of the mass within the vessel 1. The turbulent mass isspread outwardly from the center and sinks by being continuously pushedby new portions of the mass reaching the bottom part of the vessel, fromwhich it is again sucked and so on. A complex fountain-type turbulentmovement of the mass in both vertical and radial directions occurs inall zones within the vessel 1. The high speeds and the relatively largedischarge of the stirring unit insure a rapid diffusion and rapidhomogenization of the extraction fluid during this movement.

Steam for the continuous reheating, and other chemical reagents areintroduced by the injector-mixer 17 as required, such introduction beingeffected through the pipe 18, the pipe ring 19, and the jet formingholes in such ring. The agitating unit is stopped by switching off theelectric motor 20 either automatically or manually. The change of theoperation modes from low to maximum speed of rotation of the shaft 11and vice versa is effected automatically based upon a program, ormanually if desired. The propeller blade tip speed in the light or slowspeed agitation mode is from 3 to 10 m/sec, whereas in the heavy orintense mode of agitation the propeller blade tip speed ranges fromsomewhat above 10 to 25 m/sec.

The separation of the extract through outlet 6 can be done both when themotor 20 is idle or when it is rotating with a reduced speed. When theoutlet opening 6 is opened the mass begins to be drained, the liquidextract being filtered through the walls of the screen 5,5', theportions 5' of the screen assisting in the draining of the raw material.After repeating the above described extraction process several times theraw material is released from the vessel 1 through the outlet opening 4therein by opening the valve interposed in such opening.

The method of the invention is illustrated by the following non-limitingexamples.

EXAMPLE 1

8 tons of cold water was put into the extraction vessel 1, the agitatingmechanism was started by energizing motor 20, and 500 kg of dry applepressings were introduced into the vessel 1 through the charging opening8. After two minutes of agitation the motor 20 was stopped and theliquid phase was released by means of opening the valve in the outlet 6.A second batch of water warmed to 35° C. was then added for the completewashing of the water soluble matter which was drained in the same mannerafter a one minute period of agitation. Then 6.5 tons of hot (80°-90°C.) aqueous sulphurous acid solution was added with the simultaneousstarting of the agitation mechanism. Such agitation mechanism wasprogrammed for the following automatic operation: 10 min. of lightagitation, 1 min. of intensive agitation, again 10 min. of lightagitation and so on for a total of 30 minutes. During this time, themass of material within the vessel 1 was held between 75° and 85° C.,and the pH of such mass was held at pH=2.0. Corrections of thetemperature and pH values were effected by means of the injectorequipment 17. After the 30 minute period was over, the agitatingmechanism was stopped and the extract (65-75% of the liquid phase) wasdrained. Again 6.5 tons of acid extracting agent was added, and theextraction was executed again in the manner described above. After thedraining of the second extraction, the vegetable matter was removed fromthe vessel 1 by opening the outlet 4 and was delivered for pressing.

EXAMPLE 2

The apple pressings were washed in water in the manner described abovein Example 1. The difference in the extracting process from that ofExample 1 was in the fact that the first extraction instead of beingmade in fresh acid extracting agent was effected by hot extract from thesecond extraction, and the second extraction was effected by hot extractfrom the third one.

EXAMPLE 3

3 m³ of cold water water was introduced into the vessel 1, the agitatorwas started, and 500 kg of apple pressings were introduced into thevessel through opening 8. After 1 min. of agitation and 15 min. of rest,the liquid phase (6.5 m) was drained off. Then 8.5 m³ hot water (at 92°C.) was added, sulfur dioxide was added to the mass within the vessel 1until a concentration of about 0.5 n was reached, and water vapour wasadded to the vessel through the injector mixer 17 so that the masswithin the vessel reached the required temperature of 80°-85° C. Afterthe mass had reached the required parameters of acidity and temperature,the mixture was mixed for 1 min., then allowed to rest for about 30min., then was agitated for 1 min., then was allowed to rest for 30min., was agitated for 1 min. and after 60 min. of rest the extract wasdrained off through outlet 6. After 70% of the liquid phase had beendrained a new amount of water at 90° C. was fed into the vessel 1,additional sulphur dioxide was used for saturation until a value of 0.3n was reached, and if need be water and steam were fed through theinjector-mixer so that the mass reached the temperature of 70°-80° C.The extraction was then conducted in the following manner: 30 seconds ofagitation, 30 min. of rest, 30 seconds of agitation, 60 min. of rest,after which the extract was drained through opening 6. After draining70% of the liquid phase, the residual vegetable mass was discharged fromthe vessel through opening 4 at the bottom thereof.

EXAMPLE 4

8 m³ of water was poured into the extraction vessel 1, the agitator wasstarted, and 500 kg of apple pressings were added to the vessel. After 1min. of agitation and 15 min. of rest, the liquid phase (6.5 m) wasdrained through the outlet 6. Then 3.5 m³ of hot water at 92° C. wasadded. The mass was saturated by sulphur dioxide to about 0.5 n and thenwater and steam were fed through the injector-mixer 17 so that the massreached the required temperature of 80° to 85° C. After the requiredparameters had been reached, both for acid content and temperature, themixture was mixed for 20 min. after which it was sent for separation orpressing.

EXAMPLE 5

5,000 kg of fresh apple pressings were placed in the extraction vessel1, 5 m³ of water was added, and the agitator was started. The agitatorwas run initially for 1 min. of intensive operation, and then for 10min. of light agitation. Then the liquid phase (dilute apple juice) wasdrained and the pressings were sent for additional pressing andseparation of the liquid phase, and the washed pressings were dried inthe normal manner.

EXAMPLE 6

5,500 kg of fresh pressed carrots were mixed in 4.5 m³ of water in theextraction vessel 1, and the mixture was stirred intensively for 2 min.,followed by 10 min. of light agitation. Then the liquid phase (dilutecarrot juice) was drained, and the solid phase was subjected to pressingfor the separation of extra juice, and the pressings produced were driedin the normal manner.

EXAMPLE 7

This example is similar to Example 5 but with the difference in thisexample that in this example a double extraction was made initially ofdilute apple juice produced from a preceeding second apple pressingextraction, and then extraction with water was conducted.

The method and apparatus of the invention have the following advantages.

A greater accelerated diffusion is achieved in the whole extractionablevolume, due to the following-type turbulent continuous mass movement bymeans of two modes of agitation which differ in intensity, andalternately changing the mode of the propellor mechanism guaranteeinghigh relative speeds and large speed of motion of the mass. In such modetreatment, and due to the special shape and ribs of the screen 5, 5'there is achieved an accelerated and even extract separation which isconvenient for repeated extractions. This results in a shorterproduction cycle and a greater yield of the extractable matter. This isespecially true in pectin extraction, wherein the yields produced by themethod and apparatus of the present invention increase from 10 to 60% ascompared with the prior art extraction methods.

Although the invention is illustrated and described with a reference toa plurality of preferred embodiments thereof, it is to be expresslyunderstood that it is in no way limited to the disclosure of suchplurality of preferred embodiments, but is capable of numerousmodifications in the scope of the apended claims.

We claim:
 1. Apparatus for the extraction of a mass of fruit, vegetablepressings, or plant raw materials in a closed system, comprising aclosed heat-insulated vessel with an internal draining wall, a drivingunit having two driving speeds, a vertical shaft within the vesseldriven by the driving unit, an impeller mounted on the lower end of theshaft, means for rectifying the material flow, an elongated verticaldiffuser within which the impeller is disposed, the vessel having animperforate side wall, and the internal draining wall of the vesselbeing in the form of a screen spaced inwardly from the imperforate wallof the vessel, and forming an annular draining chamber therewith, andcomprising means for discharging liquid from the space between theimperforate wall and the internal draining wall thereof, the means forrectifying the material flow being disposed above the impeller in thevertical diffuser, and being in the form of a rectifying grid wherebythe material driven upwardly by the impeller travels directly upwardlywithout substantially any spin within the upper part of the verticaldiffuser.
 2. Apparatus according to claim 1, wherein the screen formingthe internal draining wall has arcuate portions spaced radially from theimperforate side wall of the vessel, such arcuate portions being ofequal angular extent and being separated by inwardly folded zones of thescreen.
 3. The apparatus according to claim 1, wherein the vessel has adownwardly converging frusto-conical bottom and the diffuser is mountedgenerally coaxial of the bottom of the vessel and has a lower, upwardlyconverging frusto-conical mass entry end disposed close to and above thecentral, lowermost part of the bottom of the vessel.
 4. The apparatusaccording to claim 3, wherein the cover has a ventilation opening and anopening therein for charging the mass of material into the vessel. 5.Apparatus according to claim 4, comprising a sprinkling tube disposedwithin the vessel inwardly of the internal draining wall, and whereinthe apparatus further comprises an injector-mixer of the Venturi pipetype which serves to inject heating fluid into the mass in the vesselvia a delivery pipe connected to said sprinkling tube.